creep and shrinkage at crack section 1

[PowerRanger]

Hi Fellows

I am designing the bearing pad support the bridge beam. And I have a question about the creep and shrinkage displacement at the bottom of the beam.

My case is, the prestress beam I designed is allow the cracking under the full loading, and my question is after the beam cracked at the bottome of the beam, will there be any more shrinkage and creep at the bottom of the beam to cause movement at the support (which betweem the beam and the pad), or the shrinkage and creep only affect the top of the beam to the neutral axis in a crack section?

In my situation, the creep by prestress at the bottom of the beam is at the same way as the shrinkage before the section crack under the dead load itself.(member hog at this time, bottom stress act compressive, so the strain is toward each other at the support). After traffic loading, the section crack, this is what I am not understand the creep and shrinkage strain movement at the support after the concrete is flexure cracked.

For designing the bearing pad size, I need to find out the shear strain due to tangential movements and forces.

Thank you

 

[jimaitken]

PowerRanger

I think you are overthinking the problem. Creep and shrinkage deflections are time dependent. The PCI handbook details how to calculate the overall deflections taking the creep and shinkage into account and what factors should be used at release, erection and final. This information is used to determine the beam seat elevation, which is critical to ensure your deck geometry is correct.
To design the bearing the beam data you need is dead and live load(no impact), thermal movement of the span(+ any sustained horizontal movement) , and the overall deflection at erection of the beam with the full deadload (non-composite) applied and the rotation of the bearing due to this loading. AASHTO 17 edition Chapter 14 details the design requirements (14.6.5 or 14.6.6 elastomeric pads Method A or B.